Method and apparatus for infrared detection and display

ABSTRACT

Embodiments of the subject invention relate to a method and apparatus for infrared (IR) detection. Organic layers can be utilized to produce a phototransistor for the detection of IR radiation. The wavelength range of the IR detector can be modified by incorporating materials sensitive to photons of different wavelengths. Quantum dots of materials sensitive to photons of different wavelengths than the host organic material of the absorbing layer of the phototransistor can be incorporated into the absorbing layer so as to enhance the absorption of photons having wavelengths associated with the material of the quantum dots. A photoconductor structure can be used instead of a phototransistor. The photoconductor can incorporate PbSe or PbS quantum dots. The photoconductor can incorporate organic materials and part of an OLED structure. A detected IR image can be displayed to a user. Organic materials can be used to create an organic light-emitting device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/865,505, filed Oct. 1, 2007, which claims the benefit of U.S.application Ser. No. 60/930,225, filed May 14, 2007, and claims thebenefit of U.S. application Ser. No. 60/848,581, filed Sep. 29, 2006,all of which are hereby incorporated by reference herein in theirentirety, including any figures, tables, or drawings.

BACKGROUND OF INVENTION

There are many applications for detecting infrared (IR) radiation. IRcan refer to radiation having wavelengths longer than visible light(>0.7 μm) up to about 14 μm, with near-IR being a subset referring towavelengths from about 0.7 μm to about 1.0 μm. One application is thedetection of IR in environments with low ambient light, which can occur,for example, at night. It can also be useful to display to a user theimage of the detected IR at a wavelength visible to the user. One commondevice for detecting IR images and displaying the detected images to auser is night-vision goggles.

Conventional night vision goggles are complex electro-optical devicesthat can require very high operating voltages and cost thousands ofdollars. Typical night vision goggles intensify existing light insteadof relying on their own light source and are sensitive to a broadspectrum of light, from visible through infrared. A conventional lens,called the objective lens, captures ambient light, including somenear-infrared light. The gathered light is then sent to animage-intensifier tube. The tube outputs a high voltage, e.g., about5,000 volts, to the image-tube components. The image-intensifier tubehas a photo cathode, which is used to convert the photons of lightenergy into electrons. As the electrons pass through the tube, similarelectrons are released from atoms in the tube, multiplying the originalnumber of electrons by a factor of thousands through the use of a microchannel plate (MCP) in the tube. When the electrons from the photocathode hit the first electrode of the MCP, they are accelerated intothe glass micro channels by the 5,000-V bursts being sent between theelectrode pair. As electrons pass through the micro channels, they causethousands of other electrons to be released in each channel using aprocess called cascaded secondary emission. These new electrons alsocollide with other atoms, creating a chain reaction that results inthousands of electrons leaving the channel where only a few entered. Atthe end of the image-intensifier tube, the electrons hit a screen coatedwith phosphors. These electrons maintain their position in relation tothe channel they passed through, which provides a perfect image sincethe electrons stay in the same alignment as the original photons. Theenergy of the electrons causes the phosphors to reach an excited stateand release photons. These phosphors create the green image on thescreen that has come to characterize night vision. The green phosphorimage is viewed through another lens called the ocular lens, whichallows you to magnify and focus the image. The night vision device maybe connected to an electronic display, such as a monitor, or the imagemay be viewed directly through the ocular lens.

Accordingly, there is a need for IR sensors/detectors, and IRsensor/detector-display combinations, that operate at low operatingvoltages and are lightweight and cost-effective to produce.

BRIEF SUMMARY

Embodiments of the subject invention relate to a method and apparatusfor infrared (IR) detection. A specific embodiment utilizes organiclayers to produce a phototransistor for the detection of IR radiation.The wavelength range of the IR detector can be modified by incorporatingmaterials sensitive to photons of different wavelengths. In a specificembodiment, quantum dots of materials sensitive to photons of differentwavelengths than the host organic material of the absorbing layer of thephototransistor can be incorporated into the absorbing layer so as toenhance the absorption of photons having wavelengths associated with thematerial of the quantum dots.

In another embodiment, a photoconductor structure can be used instead ofa phototransistor. In one embodiment, the photoconductor can incorporatePbSe or PbS quantum dots. In another embodiment, the photoconductor canincorporate organic materials.

Specific embodiments also involve displaying a detected IR image to auser. In a specific embodiment, organic materials can be used to createan organic light-emitting device. Additional material that emits atdifferent wavelengths can be added to the light-emitting layer. In aspecific embodiment, quantum dots of materials associated with emissionof photons of different wavelengths than the host organic material ofthe emission layer can be incorporated into the emission layer toenhance the output display of the organic light-emitting device to theuser. In a preferred embodiment, the IR detection is accomplished with aphototransistor and the displaying of the detected IR image isaccomplished with an organic light-emitting device such as an organiclight-emitting diode (OLED). In a more preferred embodiment, thephototransistor and OLED are in series.

Embodiments of the subject invention pertain to a method and apparatusfor night vision. In an embodiment, a night vision device can beaccomplished by the deposition of layers of organic thin films.Embodiments of the subject device can operate at low operating voltages,such as 10-15 V. In addition, the cost of manufacturing specificembodiments of the subject device can be lower than the cost ofmanufacturing conventional night vision systems. In an embodiment of thesubject night vision device an organic phototransistor can be in serieswith an organic light-emitting device, such as an organic light-emittingdiode (OLED).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an embodiment of a two-dimensional infrared imagesensor/detector, a two-dimensional infrared image sensor/display arraywithout pixelation, and a circuit model of the sensor/display array.

FIG. 2 shows a PNP bipolar phototransistor and an NPN bipolarphototransistor in accordance with embodiments of the subject invention.

FIG. 3 shows an embodiment of an infrared image/sensor display arrayusing PbSe quantum dots in the absorption layer.

FIG. 4 shows an embodiment of the subject display device incorporatingCdSe quantum dots in the emission layer.

FIG. 5 shows materials that can be used in various embodiments of thesubject invention.

FIG. 6 shows an embodiment using PbSe quantum dots as photoconductors.

FIG. 7 shows an embodiment using organic materials as thephotoconductors.

FIG. 8 shows an embodiment using a photoconductor as a light sensor.

DETAILED DISCLOSURE

Embodiments of the subject invention relate to a method and apparatusfor infrared (IR) detection. A specific embodiment utilizes organiclayers to produce a phototransistor for the detection of IR radiation.The wavelength range of the IR detector can be modified by incorporatingmaterials sensitive to photons of different wavelengths. In a specificembodiment, quantum dots of materials sensitive to photons of differentwavelengths than the host organic material of the absorbing layer of thephototransistor can be incorporated into the absorbing layer so as toenhance the absorption of photons having wavelengths associated with thematerial of the quantum dots.

In another embodiment, a photoconductor structure can be used instead ofa phototransistor. In one embodiment, the photoconductor can incorporatePbSe or PbS quantum dots. In another embodiment, the photoconductor canincorporate organic materials.

Specific embodiments also involve displaying a detected IR image to auser. In a specific embodiment, organic materials can be used to createan organic light-emitting device. Additional material that emits atdifferent wavelengths can be added to the light-emitting layer. In aspecific embodiment, quantum dots of materials associated with emissionof photons of different wavelengths than the host organic material ofthe emission layer can be incorporated into the emission layer toenhance the output display of the organic light-emitting device to theuser. In a preferred embodiment, the IR detection is accomplished with aphototransistor and the displaying of the detected IR image isaccomplished with an organic light-emitting device such as an organiclight-emitting diode (OLED). In a more preferred embodiment, thephototransistor and OLED are in series.

Embodiments of the subject invention pertain to a method and apparatusfor night vision. In an embodiment, a night vision device can beaccomplished by the deposition of layers of organic thin films.Embodiments of the subject device can operate at low operating voltages,such as 10-15 V. In addition, the cost of manufacturing specificembodiments of the subject device can be lower than the cost ofmanufacturing conventional night vision systems. In an embodiment of thesubject night vision device an organic phototransistor can be in serieswith an organic light-emitting device, such as an organic light-emittingdiode (OLED).

Preferably, electrodes that are transparent to infrared light are usedto allow IR radiation to enter the phototransistor. A schematic diagramof an embodiment of an IR sensor/detector, an embodiment of an IRsensor-display combination, and a circuit model for the IRsensor-display combination are shown in FIG. 1. A PNP bipolarphototransistor created using layers of organic material is shown on theleft of FIG. 1. Here, CuPc is the n-layer and PTCBI is the p-layer.Although the curved arrow symbolizing light (absorbing IR and emittinggreen) are shown pointing to the absorption layer and emission layer,respectively, the IR light enters from the top and the visible light isemitted from the bottom of the device shown in FIG. 1. In the middle ofFIG. 1, the integration of the phototransistor shown on the left with anOLED is shown. IR images can be incident on the top of the electrodelayer (NiO) of the phototransistor and pass through the CuPc layer andinto the absorption layer (PTCBI).

Upon photoexcitation with infrared light, charge carriers are generatedin the phototransistor and injected into the OLED, which then generatesphotons in the visible range. Because of the low conductivity of organicthin films, the electric field will be confined within the photoexcitedarea and visible photons will be generated within the excited area. As aresult, if a broad area device is exposed to an infrared image, avisible image will be generated. Preferably, an electrode transparent tovisible light is used at the bottom, where the output image is emitted.In the embodiment shown, ITO is used as an electrode, which istransparent to visible light. Other materials can also be used. Acircuit diagram of the integrated device shown in the middle is shown onthe right side of FIG. 1. In a specific embodiment, no electronics arerequired to operate the device. In an embodiment, the operating voltagesof the phototransistor and the light-emitting device are less than 10 V,such that the total operating voltages can be less than 20 V. Thisdevice can be made very light weight.

In an embodiment, glass can be used as a substrate for fabrication. Theentire phototransistor and OLED combination can be very thin, forexample, less than 1 μm. The glass substrate with the thin layer canthen be made part of night vision goggles where the thin layer ispositioned to receive an IR image and a user is positioned to see thevisible image emitted from the glass, or plastic, substrate such thatthe user receives the light emitted by the light-emitting layer as anindication of the incident IR light.

FIG. 2 shows the PNP bipolar transistor of FIG. 1 and an NPNphototransistor, which can also be utilized in accordance with thesubject invention.

The fabrication procedure for a specific embodiment of the subject IRdetector-display combination will now be described. This fabricationprocedure does not require any patterning. Other fabrication techniques,as well as other materials, as would be apparent to one skilled in theart having the benefit of the subject disclosure, can also be utilizedin accordance with the subject invention. Devices are grown on a glasssubstrate or plastic substrate precoated with a 100 nm thick layer ofindium-tin-oxide having a sheet resistance of 20 ohms/square. Substratesare degreased with solvents and then cleaned by exposure to oxygenplasma and UV-ozone ambient. All layers are vacuum deposited grown insuccession without breaking the vacuum. In the first deposition step ontop of the indium-tin-oxide (ITO) layer, to fabricate the integrated PNPphototransistor and OLED shown in the middle of FIG. 1, a 10-nm-thickCuPc is deposited as a hole injection layer. A 50 nm-thick NPD layer isthen grown and acts as a hole transport layer. Next, a 60 nm-thick Alq3emissive layer is deposited. A LiF (2 nm)/NiO (10 nm) charge generationlayer is then deposited. This results in an OLED. To fabricate thephototransistor on the top of the light emitting device, a 40 nm thickCuPc layer, a 50 nm thick PTCBI layer, a 40 nm thick CuPc layer, and a1000 nm NiO layer are then deposited.

In another specific embodiment, referring to FIG. 3, the PTCBI layer ofthe phototransistor is replaced with a PbS or PbSe quantum dot layer.The PbS or PbSe absorbs photons of different wavelengths than the PTCBIlayer. As an example, a PTCBI layer can be created that absorbs photonsup to wavelengths of about 1 μm and a PbSe quantum dot layer, or PbSquantum dot layer, can be created that also absorbs photons havingwavelengths in the range of about 1 μm to about 3 μm, so as to expand towavelength range for detection. Other wavelength ranges can beaccomplished by proper selection of the material in the absorptionlayer.

In a further specific embodiment, referring to FIG. 4, the 60 nm Alq3layer of the light emitting device from FIG. 1 or FIG. 3 is replacedwith a 50 nm Alq3 layer and a CdSe quantum dot layer. The material forthe quantum dot layer can facilitate emission of light at wavelengthsdifferent from the light emitted by the Alq3 layer. Accordingly, othermaterials can also be utilized in accordance with the subject invention.

FIG. 5 shows structures of materials that can be utilized withembodiments of the subject invention. Shown in FIG. 5 are structures fortris-(8-hydroxyquinoline) aluminum (Alq3),4-4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (NPD), copperphthalocyanine (CuPc), andperylene-3,4!8,10-tetra-carboxylic-diimide-di˜2,6-isopropy˜phenyl(PTCDI).

Although exemplary embodiments directed to a phototransistor andphototransistor/OLED combination fabricated primarily from organicmaterial layers have been described, additional embodiments can utilizeinorganic materials for the phototransistor and/or the light emittingdevice. Examples of inorganic materials that can be used to fabricatephototransistors and/or light emitting device in accordance with thesubject invention include, but are not limited to, amorphous silicon,germanium, and diamond-like carbon. Thin film amorphous silicon couldhave PbSe or PbS to absorb IR. An inorganic OLED can use ZnO to emitvisible light. The use of inorganic materials in the absorption layercan allow detection of IR with wavelengths in the range of about 1 μm to4 μm. These materials and the techniques to fabricate phototransistorsand/or OLED's with structures similar to those shown in FIGS. 1, 2, 3,and 4 are known to those skilled in the art. In this way, an inorganicphototransistor can be incorporated with an organic OLED and an organicphototransistor can be incorporated with an inorganic OLED.

Embodiments of the present invention can incorporate a photoconductor.In specific embodiments, a photoconductor can replace thephototransistor described in the above embodiments. FIG. 6 shows aphotoconductor device incorporating PbSe quantum dots. The PbSe quantumdots can be used to sense photons with wavelengths between 1 μm to 3 μm.The photoconductor structure can be formed of photoconductive materialarranged between two electrodes. In one embodiment, one electrode can beformed of gold (Au) and the second electrode can be formed of ITO. In anembodiment, PbS quantum dots can be used in the place of the PbSequantum dot layer. In operation, carriers can be photoexcited in thequantum dot (QD) layer through the absorption of IR rays. The carrierscan travel to an OLED element to emit, for example, green light. Inparticular, electrons may be injected into an emissive layer of the OLEDelement and recombine with holes to give off light.

In the embodiment shown in FIG. 6, the photoconductor can be formed onan OLED element. The OLED element can be formed on a glass substrate andcan incorporate an ITO layer formed on the substrate, a CuPc layerformed on the ITO layer to act as a hole transport layer, a NPD layerformed on the CuPc layer to act as a hole transport layer, an Alq layerformed on the NPD layer, and a LiF/NiO layer for charge generationformed on the Alq layer. The photoconductor can be formed on the LiF/NiOlayer by depositing a gold layer on the LiF/NiO layer, forming aphotoconductive material layer on the gold layer, and forming an ITOlayer on the photoconductive material layer.

FIG. 7 shows a photoconductor device incorporating organic materials.Referring to FIG. 7, one of the electrodes for the photoconductor can beeliminated when incorporated with an OLED element. In particular, thephotoconductive material can be in direct contact with a holetransporting layer of an OLED. In an embodiment, titanyl phthalocyanine(TiOPc) can be used as the photoconductive material of a photoconductordevice. The TiOPc can respond to IR rays because TiOPc absorbswavelengths at 0.8 μm. The OLED element can be formed on a glasssubstrate and can include an ITO layer formed on the substrate, aLiF/NiO layer formed on the ITO layer, an Alq layer formed on theLiF/NiO layer and a NPD layer formed on the Alq Layer. Thephotoconductive material can be formed directly on the NPD layer withoutan intervening electrode.

FIG. 8 shows an embodiment incorporating a photoconductor as the lightsensor. A photoconductor can have very large gain or amplification andis ideal to amplify the signal. The photoconductor device includes twolayers, a charge transport layer and a sensitizer. NPD can be used as acharge transport layer and PbSe, PbS, and/or InAs quantum dots can beutilized for photon absorption.

In operation, carriers can be photoexcited in the TiOPc layer. Thecarriers can travel to the OLED element to emit, for example, greenlight. In particular, holes can be injected into the NPD layer torecombine with electrons and give off light.

In embodiments of the present invention, the gain in photoconductors canbe as large as 100,000.

For embodiments incorporating photoconductors instead ofphototransistors, fabrication may involve less process steps due toembodiments of photoconductors being single layer devices instead of athree-layer NPN or PNP structure.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

The invention claimed is:
 1. A method of detecting infrared (IR),comprising: providing an IR detector, wherein the IR detector comprises:an absorbing layer; a light-emitting layer, wherein at least one of theabsorbing layer and the light-emitting layer comprises an organicmaterial; an organic light emitting diode (OLED), wherein the OLEDincorporates the light emitting layer, a first electrode transparent toinfrared light; and a second electrode, wherein IR light to be detectedpasses through the first electrode transparent to IR light and entersthe absorbing layer, wherein the IR light is absorbed in the absorbinglayer so as to generate photoexcited charge carriers, wherein the chargecarriers are injected into the organic light emitting diode so as togenerate photons, wherein the second electrode is transparent to thegenerated photons, wherein the generated photons pass through the secondelectrode, wherein the generated photons are in the visible range, andwherein the generated photons passing through the second electrodeproduce a visible output image corresponding to an infrared imageincident on the first electrode, incidenting IR light on the IRdetector; and receiving light emitted by the light-emitting layer as anindication of the incident IR light.
 2. The method according to claim 1,wherein the IR detector comprises a photoconductor, wherein thephotoconductor incorporates the absorbing layer.
 3. The method accordingto claim 1, wherein the absorbing layer comprises the organic materialand quantum dots of materials sensitive to photons of differentwavelengths than the organic material of the absorbing layer.
 4. Themethod according to claim 1, wherein the light-emitting layer comprisesthe organic material and quantum dots of materials associated withemission of photons of different wavelengths than the organic materialof the light-emitting layer.
 5. The method according to claim 1, whereinthe IR detector comprises a display for displaying an output image to auser, wherein the display incorporates the OLED.
 6. The method accordingto claim 1, wherein the absorbing layer comprises PbSe quantum dots. 7.The method according to claim 6, wherein the IR detector allowsdetection of wavelengths in the range of about 1 μm to about 3 μm. 8.The method according to claim 7, wherein the IR detector comprises aphotoconductor, wherein the photoconductor incorporates the absorbinglayer, wherein the photoconductor and OLED are in series.
 9. The methodaccording to claim 8, wherein the photoconductor is in direct contactwith a hole transporting layer of the OLED.
 10. The method according toclaim 1, wherein the absorbing layer comprises PTCBI.
 11. The methodaccording to claim 1, wherein the emitting layer comprises Alq3.
 12. Themethod according to claim 1, wherein the emitting layer comprises a CdSequantum dot layer.
 13. The method according to claim 1, wherein theabsorbing layer comprises PbS quantum dots.
 14. The method according toclaim 1, wherein the absorbing layer comprises the organic material,wherein the light-emitting layer comprises an inorganic material. 15.The method according to claim 14, wherein the IR detector allowsdetection of wavelengths in the range of about 1 μm to about 4 μm. 16.The method according to claim 1, wherein the light-emitting layercomprises the organic material, wherein the absorbing layer comprises aninorganic material.
 17. The method according to claim 1, wherein theabsorbing layer and the OLED are positioned between the first electrodeand the second electrode.